Concentration of neuropeptide Y, galanin, &bgr;-endorphin, vasoactive intestinal peptide and gonadotropin releasing hormone in the hypothalamus of gilts during the estrous cycle.

: Numerous reports indicate that peptides isolated from the brain such as beta-endorphin (beta-END), neuropeptide Y (NPY), galanin (GAL) or vasoactive intestinal peptide (VIP), modulate secretion of gonadotropins and prolactin. The objective of the present experiment was to determine concentrations of NPY, GAL, beta-END, VIP and GnRH in the preoptic area (POA), medial basal hypothalamus (MBH) and pituitary stalk-median eminence (SME) during the estrous cycle in the pig. Gilts were slaughtered on Days 5, 10, 15 and 20 of the estrous cycle. Blood samples for analyses of progesterone were taken before slaughter. Neuropeptide concentrations in brain tissues were determined using RIA. The highest concentrations of all determined peptides occurred in SME. GnRH concentration in MBH was lower (p<0.05) in POA and SME on Day 20 than on Day 5. NPY concentration in POA was 5-6 times greater (p<0.05) on Days 10 and 20 than on Day 5. Similarly, concentrations of VIP in POA were greater (p<0.05) on Day 10, Day 15 and Day 20 than on Day 5. The concentration of GAL in POA was higher on Days 10 and 15 (p<0.05) than on Days 5 and 20. The concentration of GAL in SME was lowest on Day 5 and then significantly increased on Days 10, 15 and 20. In SME, concentration of beta-END increased 10 times on Days 15 and 20 when compared to Day 5 of the cycle. The correlation between concentration of GAL in the POA and MBH and progesterone concentration in the peripheral blood was positive, whereas this correlation associated with the SME was negative. These results indicate that considerable changes in various neuropeptide concentrations in different areas of the porcine hypothalamus are associated with stage of the estrous cycle and that GAL may be involved in control of the preovulatory LH surge in pigs.